The present invention relates to structure of a watch casing provided with a wrist band switch.
Japanese Utility Model Registration Application laid-open publication no. 156625/1985 discloses the conventional casing structure in which a flexible substrate of a switch is incorporated into a wrist band of the watch. FIG. 4 shows this conventional structure. In forming the wrist band, first a primary piece 13a is molded and a switch member 7 is disposed under the primary piece 13a. Thereafter, a lower secondary piece 13b is molded integrally with the primary piece 13a.
The switch member 7 is held at its one end portion by a holding member 11 which is formed inside the wrist band. Further, the primary piece 13a on the switch member is formed with protrusions 13c effective to maintain a spacing relative to the switch member.
However, the FIG. 4 structure has three drawbacks. The first drawback relates to forming of the wrist band. Since the molding of the secondary piece 13b is effected under the state where the switch member is attached to the primary piece 13a, the switch member is exposed directly to heated and melted resin during a secondary molding operation. Further, since the melted resin is flown closely around the switch member, and is cured and shrinked, considerable friction may be caused between the band pieces and the switch member when bending the finished wrist band, thereby hindering flexibility of the wrist band. After repeating the bending of the wrist band during the course of use, the switch member may be broken.
The second drawback is caused by the fact that the holding member of the switch member is formed within the wrist band. In such structure, the switch member could not be incorporated into a cavity of the wrist band after molding. Thus, in the conventional structure, the secondary molding operation must be carried out while super posing the primary band piece and the switch member with each other. Therefore, replacement of the switch member cannot be effected other than cutting the wrist band.
The third drawback is such that the protrusions are integrally formed with the upper band piece in order to maintain a spacing between the upper band piece and the switch member. These protrusions are provided as a spacer, because the upper band piece is stretched to apply pressure toward the lower band piece when the wrist band is bent due to deformation rate difference between the upper and lower band pieces. However, these protrusions are easily dislocated relative to the switch member while bending of the wrist band to thereby impair its spacing function. Therefore, the switch member may be inadvertently operated to cause erroneous input operation of the switch member.